The present invention relates to a multiplexing transmission system in which packet data is inserted into a sound-silent period of a digitized speech signal and in which other data is multiplexed with the digitized speech signal.
In this type of multiplexing transmission system, wherein data is transmitted as packet data, it is necessary to form data into a packet and later extract it from the packet. This requires a relatively long transmission response time. However, some data requires a quick response to provide transmission without substantial delay. Therefore, this method is not suitable where a quick response is required.
The present invention provides a multiplexing transmission system which is suitable for data transmission requiring a quick response and which can achieve a high transmission efficiency.
A prior art multiplexing transmission system transmits packet data in a sound-silent period of prior art system. A speech detector 1' detects sound-existing/sound-silent periods of digitized speech. A selector 21 passes speech when the output (sound-existing/sound-silent) from detector 1' indicates a sound-existing period and passes packet data (PKT) when the output from detector 1' indicates a sound-silent period. Multiplexer 3 arranges the output of selector 21 and the output of speech detector 1' in a time sequence. This explains the structure of the transmission side A. Speech, packet data (PKT) and a sound-existing/sound-silent bit are multiplexed with priority given to speech, and the multiplexed signal is transmitted to the receiving side B through transmission path 6.
On receiving side B, a demultiplexer (DEMUX) 71, a distributor 72, a selector 22 and a noise generator 8 are provided. The DEMUX 71 separates the sound-existing/sound-silent bits from the speech/PKT data. The distributor 72 is switched by the extracted sound-existing/sound-silent bits so that when a sound-existing bit is present, the signal at that time, namely, speech, is transmitted to the selector 22, and when a sound-silent bit is present, the signal at that time, namely, the PKT, is transmitted to the output terminal. The selector 22 is also switched by a sound-existing/sound-silent bit. The selector 22 selects speech output from the distributor 72 in response to the sound-existing bit, and selects the output of the noise generator 8 in response to a sound-silent bit. In this manner, the speech and packet data are subjected to a separation and extraction on the receiving side and noise is inserted into a sound-silent period, thereby forming a similar signal to that on the transmitting side. In the multiplexing system of FIG. 1 speech is given priority and data is formed into a packet. This system cannot process data which requires a quick response, thus there is no way of transmitting data other than by separately providing a simple multiplexing method, i.e. by providing an exclusive time slot. However, if this separate time slot is used only for data which are not subjected to a packet, nothing is transmitted during a data-absence period. As a result, the total transmission efficiency is not improved.